Disintegrins have been shown to bind cell surface molecules, including integrins, on the surface of various cells, such as platelets, fibroblasts, tumor, endothelial, muscle, neuronal, bone, and sperm cells. Disintegrins are unique and potentially useful tools for investigating cell-matrix and cell-cell interactions. Additionally, they have been useful in the development of antithrombotic and antimetastatic agents due to their anti-adhesive, anti-migration of certain tumor cells, and antiangiogenesis activities.
Families of proteins which have disintegrin domains include ADAMs (A Metalloprotease and Disintegrin), MDCs (Metalloprotease/Disintegrin/Cysteine-rich) and SVMPs (Snake Venom Metalloprotease).
For a review of ADAMs, see Wolfsberg and White, Developmental Biology, 180:389-401, 1996. ADAMs have been shown to exist as independent functional units or in conjunction with other members of this family in heterodimeric complexes. Some members of the family exist in multiple isoforms which may have resulted from alternative splicing. ADAMs proteins have been shown to have adhesive as well as anti-adhesive functions. Some members of the ADAMs family have very specific tissue distribution while others are widely distributed. Not all members of this family are capable of manifesting all of the potential functions represented by the domains common to their genetic structure.
The ADAMs are characterized by having a propeptide domain, a metalloprotease-like domain, a disintegrin-like domain, a cysteine-rich domain, an EGF-like domain, and a cytoplasmic domain.
A prototypical example of this family is ADAM 12. ADAM 12, also known as meltrin .alpha., has a truncated isoform, as well as a full-length isoform, and is involved in muscle cell fusion and differentiation (Gilpin et al., J. Biol. Chem. 273:157-166, 1998).
Another prototypical example of this family is ADAM 1, which forms a heterodimer with ADAM 2 and is involved in sperm/egg fusion (Wolfsberg and White, supra).
The SVMP family is represented by three classes (P-I, P-II, and P-III). All three classes contain propeptide and metalloprotease domains. The P-II and P-III classes also contain a disintegrin domain, and the P-III class further contains a cysteine-rich domain. These domains are similar in sequence to those found in the ADAMs. Some members of the SVMP family have a conserved "RGD" amino acid sequence. This tripeptide has been shown to form a hairpin loop whose conformation can disrupt the binding of fibrinogen to activated platelets. This RGD sequence may be substituted by RSE, MVD, MSE, and KGD in P-II SVMPs, and by MSEC, RSEC, IDDC, and RDDC (a tripeptide along with a carboxy-terminal cysteine residue) in P-III SVMPs. Thus, these sequences may be responsible for integrin binding in the P-II and P-III SVMPs.
A prototypical example of a SVMP is jararhagin, which mediates platelet aggregation by binding to the platelet .alpha..sub.2 subunit (GPIa) via the disintegrin domain followed by proteolysis of the .beta..sub.1 subunit (GPIIA) (Huang and Liu, J. Toxicol-Toxin Reviews 16: 135-161, 1997).
The proteins of the Metalloprotease/Disintegrin/Cysteine-rich (MDCs) family are involved in diverse tasks, ranging from roles in fertilization and muscle fusion, TNFa release from plasma membranes, intracellular protein cleavage, and essential functions in neuronal development (Blobel, Cell 90:589-592, 1997). This family is also characterized by the metalloprotease, disintegrin and cysteine-rich domains, as described above.
The present invention provides a novel disintegrin homolog and related compositions whose uses should be apparent to those skilled in the art from the teachings herein.